Supersymmetric dark matter in the light of LEP 1.5

We discuss the lower limit on the mass of the neutralino χ that can be obtained by combining data from e+e− annihilation at LEP and elsewhere with astrophysical and theoretical considerations. Loopholes in the purely experimental analysis of ALEPH data from the Z0 peak and LEP 1.5, which appear when μ < 0 for certain values of the sneutrino mass mν and the ratio tan β of supersymmetric Higgs vacuum expectation values, may be largely or totally excluded by data from lower-energy e+e− experiments, the hypothesis that most of the cosmological dark matter consists of χ particles, and the assumption that electroweak symmetry breaking is triggered by radiative corrections due to a heavy top quark. The combination of these inputs imposes mχ ≥ 21.4 GeV, if soft supersymmetry-breaking masses are assumed to be universal at the grand-unification scale.